Tony Blair has defended his controversial anti-terror proposals, warning that it would be wrong to wait for an attack before acting.
'It would be a dereliction of duty to wait for a terrorist attack'
Writing in the Daily Telegraph, he conceded that plans to detain suspects under house arrest without trial were "difficult issues for any government".
The Commons has approved the measures despite considerable opposition.
But Mr Blair insists: "There is no greater civil liberty than to live free from terrorist attack."
Tory leader Michael Howard has accused Mr Blair of steamrolling the house arrest plans and of "using national security for political point scoring".
Liberal Democrat leader Charles Kennedy says that the plan is a further example of Labour's "authoritarian" response to crises.
In their first vote on the plans on Wednesday, MPs approved the proposals by 309 votes to 233, facing off opposition from the Tories, Lib Dems and 32 Labour rebels.
The government's usual majority of 161 was substantially reduced, with several Labour MPs abstaining.
The Prevention of Terrorism Bill proposes "control orders", which as well as house arrest could impose curfews, tagging or bans on telephone and internet use.
They would replace current powers to detain foreign terror suspects without trial, which the law lords have ruled against.
But critics are concerned that it would be the home secretary and not judges who decided to impose control orders.
The plans face further Commons scrutiny on Monday before passing to the Lords.
In Thursday's newspaper article, the prime minister makes it clear he regards protecting the public from terrorism as his highest duty - above safeguarding civil liberties.
He said he "rejected completely" the argument the plans were an attack on long-standing civil liberties.
"As the Bill makes clear, no-one will be deprived of their liberty without this being approved within days - at most seven days - by a senior judge in the High Court," he said.
This would be followed by a full High Court hearing, with full rights of appeal, he added.
The prime minister said he had agreed to look into Liberal Democrat leader Charles Kennedy's concerns over whether it should be the home secretary or a senior judge who initiated a control order.
But he said it was impossible to address Tory concerns, as they rejected control orders as "fundamentally flawed" and would not accept there would always be a small group of suspects who could not be prosecuted through the normal criminal process.
It was difficult to balance public protection with civil liberties but, he said, it would be "the gravest dereliction of duty to wait until we suffered a terrorist attack here, and only then act".
The government's position was not "arrogant", as Conservative leader Michael Howard had claimed, said Mr Blair, but "responsible".
Home Secretary Charles Clarke has already agreed to give judges the power to review the orders, and on Wednesday indicated he could be prepared to go further, offering to look again at the issue before Monday's vote.
The control orders 'would be open to scrutiny by the courts'
Defending the proposals, Mr Clarke reminded MPs that the Madrid bombings had taken place during the Spanish general election campaign in March 2004.
"Maybe such things can always be possibilities here too," he said.
The issue has provoked heated debate, with Mr Blair accused of steamrolling through "authoritarian" plans.
Mr Howard said the powers were being "rammed through Parliament" unnecessarily.
There are currently 11 detainees being held without trial, mostly at Belmarsh prison in east London.
They will be freed when the existing powers expire on 14 March and Mr Clarke says he does not currently intend to use the house arrest powers.
Speaking after the vote Shami Chakrabarti, director of Liberty, said with just a few days to defeat the "misguided bill" principled politicians should not compromise core democratic values.
"Punishment without sight of charges, evidence or proof is not improved by the fig leaf of judicial supervision," she said.